Nissan Navara: Increased fuel consumption

I BOUGHT a new 2.5-litre Nissan Navara D40 in July, and recently the fuel consumption increased dramatically. It had been 10.6 litres/100km in town and 8.3 litres/100km on the highway. Now its 16 and 12.3 respectively. My dealer tried to tell me this was within spec, but after pointing out the label on the windscreen saying 9.5 litres/100km they agreed 12 litres/100 km-plus did sound a little high. They have reset the injector pump, which has made no difference. They basically told me they have done all they can.